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PGRO give timely advice on desiccation of combining peas and field beans

Ideally, both combining peas and field beans are direct combined without the need for desiccation as this adds to costs and application causes crop loss.

jim scrimshaw

Jim Scrimshaw – PGRO Principal Technial Officer

“Ideally, both combining peas and field beans are direct combined without the need for desiccation as this adds to costs and application causes crop loss,” advises Jim Scrimshaw, PGRO Principal Technical Officer. “However, this is not always possible, and some crops which are weedy and/or are ripening unevenly will benefit from the timely use of an appropriate product to maintain quality.

“When it comes to choosing a chemical desiccant in peas and beans, the choice is generally between glyphosate and diquat, primarily these will be the ones considered here. There are, however, glufosinate ammonium products also approved.

“Don’t forget that desiccants bring the prospective harvest date forward – they don’t speed up seed maturity. The chemical terminates growth when development is complete allowing a smoother harvest; and harvest planning and can prevent the setting of weed seed.”

Both glyphosate and diquat are non-selective materials Diquat is a true desiccant whilst glyphosate is more a pre-harvest herbicide. A true desiccant rapidly kills above ground growth of both crop and weeds allowing rapid drying and earlier harvest (between 3-7 days after application). It will not give long-term weed control –  particularly of perennials – whereas glyphosate will.

Where persistent perennial weeds are a problem, glyphosate is the product of choice as it is a translocated herbicide acting on plant meristems. Crop effects take longer to materialise and harvest is brought forward more slowly (10 -14 days) compared to diquat.

Glufosinate ammonium products are mainly contact acting, but there is some translocation within the leaves. Crops are ready to harvest 10 -14 days after application.

A good coverage of diquat on crop and weeds is essential and it works best when the crop is beginning to senesce. Activity is dependent on temperature and UV light levels while glyphosate needs plants to be actively growing for the best effect.

Timing of the applications is very important. If desiccation takes place too early then effects can be uneven, stems can de-lignify and crops collapse reducing recoverable yield. Quality may suffer – this is more of a problem with peas – possibly increasing undersized grain and greater chances of shelling out due to the longer delay before combining. Diquat tends to work better on dicot plants (peas and beans) and glyphosate on monocots (cereals).

“Applications of diquat should be made to pea crops which are turning yellow. The bottom pods should be parchment like and the seed hard; pods in the middle should be becoming parchment like, the seed rubbery and squeezable between finger and thumb without splitting; top pods should still be fleshy green /yellow with seed that splits when squeezed.

“If glyphosate is to be used, a crop moisture content of around 30% is suggested before application.

“Desiccation has a slow effect on the relatively thick green stems of field beans and applications should be made when 90% of pods are dry and black. It is suggested that in beans glyphosate should be used specifically as a pre-harvest treatment to control perennial weeds.

“And remember that neither glyphosate or glufosinate ammonium products should be used on crops intended for seed,” adds Jim Scrimshaw.


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